Reiter



Sept. 8, 1959 F. REITER PROCESS FOR MAKING SPARK PLUGS Filed June 8. 1954 INVENTOR- PROCESS FOR MAKING SPARK PLUGS Friedrich Reiter, Schweint'urt, Germany Application June 8, 1954, Serial No. 435,256

Claims priority, application Austria June 16, 1953 4 Claims. (Cl. 29--25.12)

The present invention relates to spark plugs of the type used in internal combustion engines.

More particularly, the present invention relates to spark plug shells and a process for manufacturing these shells and locating the same on the spark plugs.

One of the objects of the present invention is to greatly reduce the cost of manufacture of spark plugs.

Another object of the present invention is to eliminate the need for gaskets and the like in spark plugs.

A further object of the present invention is to provide a spark plug shell whose heat conductivity may be easily regulated.

An additional object of the present invention is to provide a process for making a spark plug shell having a construction identical with conventional spark plug shells but whose cost of manufacture is far less than that of conventional spark plug shells.

With the above objects in view the present invention mainly consists of a process for manufacturing spark plugs, this process including the step of sintering a powdered metal into the form of a spark plug shell. This shell may be sintered directly about the insulator with or without a coating of copper located between the insulator and the shell, and similarly a coating of copper may be placed on the outside of the shell.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, in which:

Fig. 1 shows one form of spark plug construction in accordance with the present invention, with the shell of Fig. 1 shown in section to more particularly illustrate the invention; and

Fig. 2 shows an embodiment of the invention different from that of Fig. 1.

Conventional spark plugs for internal combustion engines consist essentially of an insulator along whose central axis the center electrode of the spark plug extends, and an electrically conductive shell is located about the insulator and connected to the ground electrode of the spark plug. This insulator extends through the shell and is sealed with respect thereto in a fluid-tight manner through the medium of gasket rings made of copper.

The shell which is usually made of steel is usually manufactured from a hexagonal bar stock on suitable lathes or the like. The gasket rings are manufactured from copper sheet and must be mounted separately.

Furthermore, spark plugs are known which are manufactured by pouring the insulator in liquid form into the finished shell or by pressing the insulator in powdered form into the finished shell. With such spark plugs, it is essential that the insulator material have a melting point which is lower than that of the shell. Furthermore, spark plugs are known according to which the shells are nited States Patent 2,902,747 Patented Sept. 8, 1959 ICC made from sheet metal and the insulators are pressed or rolled into these sheet metal shells in a known way. Also, there are spark plugs where the shell is sprayed in liquid form about the insulator. In modern spark plugs the insulators are made of aluminum oxide which are sintered at a temperature higher than 1800 C.

According to the process of the present invention the spark plug is manufactured by placing about the finished insulator, which, for example, may be made of a material such as the above-mentioned aluminum oxide, a metal powder and pressing this powder with heat about the insulator so as to sinter the powder and thus form a sintered shell directly on the insulator. When steel in powder form is used in the sintering process of the invention, the sintering temperature is between 1100 C. and 1200 C., this temperature of course being well below the temperature at which the insulator is sintered so that the sintering of the shell does not have any undesirable influence on the insulator. Thus, the present invention differs basically from known spark plugs and processes for making the same in that the shell is pressed about the insulator to form a particularly good seal between the shell and the insulator. A multiple part sintering mold which may be quickly assembled and disassembled'is used in the manufacture of the spark plug of the invention, the finished insulator, together with the center electrode therein, being placed within this form and a suitable metal power, such as a steel powder, being pressed about the insulator and sintered thereto according to conventional sintering processes. The ground electrode may be mounted in the form to be simultaneously sintered to the shell together with the insulator or the mold may have a shape which forms the powdered metal into a ground electrode extending from the shell.

Thus, Fig. l of the drawings shows an insulator 10 having a center electrode 11 passing therethrough, this center electrode being, for example, threaded into the insulator 10 and being adapted to carry a terminal at its top free end in a known way. The shell 12 is directly sintered to the insulator 10 according to the abovedescribed process and the ground electrode 13 is formed also according to the above-described process. The form in which the shell is sintered may be hexagonal to provide the shell with an outer hexagonal surface to receive a wrench, and the only step required after the sintering of the shell 12 is to provide the latter with the threads 14 so that the spark plug may be mounted on an internal combustion engine in a known way.

It is also possible in accordance with the present invention to provide on the outer surface of the insulator a metallic coating, preferably of copper, before the shell is sintered to the insulator. This coating being either galvanized 0r sprayed onto the insulator. Thus, Fig. 2 shows a second embodiment of the invention wherein the parts 10 and 11', 12', 13 and 14 are identical with parts 1014 of Fig. l, the embodiment of Fig. 2 having a coating 15 of copper located between and in contact with the insulator 10 and the shell 12'.

The sintering of the iron or steel powder, or othersuitable metal powder, about the finished insulator provides an extremely good bond between the shell and insulator. After the one piece shell is thus formed according to the present invention it may be immersed in a molten metal having a melting point below that of the shell, this molten metal being, for example, copper. In this way the pores of the sintered and pressed shell are closed and the thermal conductivity and specific heat of the shell are influenced. The closing of the pores produces an absolute gastightness and the insulator is all the more joined in a sealed absolute gas-tight manner to the shell if, as was mentioned above, the insulator is provided with a metallic coating prior to being joined to the shell. In this way,

all additional 1 known expedients for providing this seal are eliminated. The second action, namely the influencing of the thermal propertiesof the spark plug, enables the spark plug manufactured accordin'g'to the inventionto behave thermally in "*a predictable mannen Thus; it is possible to control with the' pro'cessof the invention the thermal properties of the spark plug to a fai greater'eX- tent =than is possible with known spark plu'gsyand the thermal control ofthe invention may 'becombined with known exp'edientssuch as-variations in the len'gth of-the insulator of the"-spa1'"k plug, etc.

and it is thereforenot possible-to varythe=heat conduc- All known shells are made of a single homogeneous material,-part-icularlysteel,"

tivity andspecific heat of the shell with these known con'-" structions.

Ac'cording to the process of the invention through varying-the force of the sintering pressure-andthrough varying-the'size of the-particles which are'sintered together and the form of these particles the' degree of porosity canbe'regulated. If the pores of the shell are filled with a metalwh'ich has a betterhe'atconductivity than that of the metal powder ofthe'shell, then the 'heat conductivityof the shell can be' ve'ry greatly'improved. For example,-

the heat-conductivity of a low'alloy steel at C: is-

between 40"and 50 kc'al.'/mh C., while the heat-conduc ivity of copper is 320. Thus-, by combining steel and cop-'- per in the shell, as by forming the shell of sintered steel powder and'fillirig the pores'thereof'with copper, it is pos-- sible to provide the shell with a heat "conductivity of be tween 70 and 140k Aside from the-physical advantages of the'spark plug of the invention, the manufacturing costs are greatlyre duced because it is unnecessary to'take into account any lossof'material-and except for the outerscr'ew' threads of the shell, the'spark plug of the inventionis completed when it is removed from the sinteringpress. The threads are formed in a known way preferably afterimmersing of the shell in a molten metal, if the shell is covered with a metallic'coating in'this 'way; Furthermore, with the process of 'theinventionthe necessity for gaskets are' eliminated as well asthe'necessity of assembling these gaskets with the'remaining members of thespark plug,

so that the spark plug of the invention is also less expeu sive for these reasons.

Instead of sinteringda powdered metal about a com-' liquid metal bath, to seal andperhaps fill the pores' of the sintered shell, can be'avoided'if the powdered metal is made up of a mixture of a plurality of metals, such as two difierent metals having different melting pointsand having the metal of the lower melting point forming the minor part of the mixture;

When the shell is made separately from the insulator according to a sintering process,in accordancewithth'e present invention,-this-shell differs from known shells only in that it is far less expensive to manufacture and in that the thermal conductivity may be regulated in the above-described manner. The control of the heat conductivity and low specific heat obtainable with shells constructed in accordance with the present invention enable the shape of the shells to be very favorably influenced when making spark plugs of different thermal properties.

It will be understood that each of the elements described above, or two or more together, may also find a useful application 'in other types of spark plugs differing from the types described above.

Whilethe invention has been illustrated and'described as embodied in sparkplugstand processfor making same, it is not intended to be limited to the details shown, since various modifications and structural changes may be made Without departing in. any Way from the spirit of the present invention.

Without further analysis, the forgoingwill so fully reveal the' gist ofthe present invention that others can by applying current knowledge readily'adapt it for various applications" without omitting features that, from the standpointofprior art, fairly constitute essential characteristics ofthe' generic orspecific aspects of this inventionand, therefore; such adaptations should and are intended to be' comprehended within the'meaning and range of equivalence of "the following" claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. In a process for manufacturing spark plugs, the step ofs'in'tering' a powdered metal about a spark plug insul ator' to forrna shell for the spark plug.

2. In a process for manufacturing spark plugs, the steps of sintering a powdered metal about a spark plug insulator to'form a shell for the spark plug; immersing the shell in a metal bath; and removing the thus immersed shell from'the' bath so as to leave a coating of metal thereon which influences the thermal properties of the shell as wellas seals the pores thereof.

3. Ina process for manufacturing spark plugs, the steps of providing on the outer surface of a spark plug insulator a coating of metal; and sintering a spark plug shell about the insulator onto said coating of metal.

4. In a process for manufacturing spark plugs, the steps of providing on the outer surface of a spark plug insultor' a coating of'metal; sintering a spark plug shell about the insulator onto said coating of metal; immersing the shell in a bath of liquid metal; and removing the shell from the metal bath so as to leave on the outside of the housing a coating of the metal of the liquid bath.

References Cited in the file of this patent UNITED STATES PATENTS 1,306,834 1 Owens June 17, 1919 1,331,091 Becker Feb. 17, 1920 1,362,773 Brewster Dec. 21, 1920 1,723,026 Ford Aug. 6, 1929 1,760,586 Devers May 27, 1930 2,373,405 Lowit Apr. 10, 1945 2,376,706 Lum May 22, 1945 2,778,742 Shipe Jan. 22, 1957 

